1. Field of Use
The present invention relates to an arrangement for maintaining means of communication between a main station and various communications centres, the means in question being capable of conveying messages at different speeds using transmission methods which will be explained below. This arrangement, which allows considerable savings in time to be made, is particularly suited to the data-processing field.
2. Prior Art
In the more and more widely used technique of remote processing, information exchanged between the central unit and the terminal systems is exchanged over very long distances at very high speed. Remote processing is used at the present time by banks for operations carried out between a head office and its branches, by transportation companies to reserve seats, and in telegraphic dealings between a central unit and remote terminals.
The items of information, which are transmitted in binary code or bits, grouped into messages are conveyed at different speeds and by different methods. The "asynchronous" method of communication may be used in which each character in a message is made up from a number of bits plus a so-called "start" signal which precedes the character and a so-called "stop" signal which follows it. The "synchronous" method of communication may also be used. With this method one or more synchronizing characters are placed at the beginning of the message, on the one hand to synchronize the clock used in sampling the bits in the message, and on the other hand to identify at the receiving apparatus, the beginning of the message following the synchronizing characters. Synchronizing characters may also be transmitted so as to keep a transmitter and a receiver synchronized.
In the majority of systems for transmitting information between a processing unit and distant terminals, communications means are provided to adapt the characteristics of the interfaces associated with each line of communication to those of the interfaces associated with the processing unit. These means are arranged in series with each line and are generally known as communications adapters.
Upon reception, the adapters receive the bits from the lines at different speeds, and transmit them to the processing unit. Upon transmission, the bits intended for the various lines are directed by the processing unit to the adapters, which then transfer them to the appropriate lines. Each adapter may have a buffer register which may be capable of containing a number of characters.
Transmission systems become more complicated when the question is one of maintaining or checking the operation of the communication means and in particular the operation of the adapters. The maintenance system which allows the operation of the adapters to be checked in fact needs to contain circuits, the complexity of which is related to the method of operation used by the adapters which it has to check. These adapters are of differing types depending on whether communication is synchronous or asynchronous, the selected speed of communication, the number of bits per character in the message, and the length of the "stop" signal. Thus, if a user wishes to add a new type of terminal at the end of a line which communicates with the processing unit, it is first of all necessary for the existing adapter on this line to be replaced by another adapter suitable to the new type of communication between the terminal and the processing unit. More importantly, it is necessary to modify the maintenance system to allow this new adapter to be checked. Added to this is the necessity for an adapter to be disconnected physically from its associated line when its operation is to be checked. This means an unfortunate loss of time to the user and may also require the presence of an engineer.
It is an object of the present invention to substantially reduce or overcome the above drawbacks and in particular to make it possible to provide a choice between various methods of communication without the necessity for altering the maintenance arrangement or physically disconnecting the communications line associated therewith when it is desired to check same.
It is another object to provide rapid maintenance at reduced cost.
It is still a further object to provide an arrangement for maintaining means of communications between a main station and various communications centres including transmission and reception circuits and for controlling a communication line between the main station and a terminal.